The present invention relates generally to a print head for an ink jet printer that projects ink for marking a substrate with the ink, and more particularly to a self-cleaning print head that automatically applies solvent to the nozzle area of the print head.
Conventional continuous ink jet printers supply electrically conductive ink under pressure to a drop generator, which has an orifice or orifices (nozzles) that are typically arranged in a linear array. The ink discharges from each orifice in the form of a filament, which subsequently breaks up into a droplet stream. Individual droplets in the stream are selectively charged in the region of the break off from the filament, and these charged drops are then deflected as desired by an electrostatic field. The deflected drops may proceed to a print receiving medium, whereas undeflected drops are caught in a gutter or catcher and recirculated.
After the printer is shut down for a period of time, ink around the orifices dries up, often partially blocking, and sometimes completely clogging, the outer openings to the orifices. Furthermore, during a long shut down period, such as an entire day or weekend, the dried ink may form a block within the orifice or passages attached to the orifice, depending on the type of ink.
Known print heads, such as that disclosed by U.S. Pat. Nos. 5,877,788 and 4,528,996, use a fluid wash that seeps over the orifices and a front face of the print head to clean away unwanted residue. This type of known print head, however, requires a certain positioning of the print head for cleaning because gravity is used to flow the cleaner along the orifices. For this reason, these types of print heads are impossible to clean in many industrial applications where omnidirectional orientation of the print head is required.
Additionally, since the solvent flows downwardly by gravity, a relatively large amount of solvent is needed to clean the front face of the known print heads because there is relatively little pressure. However, since solvent used for cleaning is recycled within the ink system, it is important that the quantity of solvent used for cleaning be low compared with the quantity of ink in the ink system. Otherwise, the ink control system may not be able to properly maintain ink composition or viscosity after orifice washing is performed.
Other conventional print heads only use a complicated mechanism that faces the front face of the nozzle to clean the outside of the orifices. Such mechanisms enclose a chamber with a shutter at the front face and flood it with cleaning fluid. However, these types of cleaning systems still typically require gravity to empty the chambers. Another type of mechanism uses a receptacle, cartridge or chamber opposing the orifices on the exterior of the drop generator for catching ink or solvent sprayed from the nozzles during a cleaning run or for suctioning ink from the nozzles. These types of mechanisms are difficult to use or are very complex, such as when the orifices are in fact in a deflection chamber behind or between ground plates and deflection plates that would have to be removed, avoided or integrated for cleaning. This type of complex system is disclosed in commonly owned U.S. patent application Ser. No. 09/162,611.
Other known print heads directed to cleaning out the inside of the orifice spray solvent or ink for cleaning through the orifice in the same direction as the ink is sprayed for printing. Another type of print head flows ink or solvent through a chamber behind the orifices in order to create suction in the orifices to pull residue into the orifices to be carried away with the solvent or to create a cross flow to prevent clogging, such as the cross flow nozzle system disclosed in U.S. Pat. No. 5,980,034. Neither of these procedures are completely effective because they do not clean the surface of the front face near the orifices where other residue can eventually collect and block the outer openings to the orifices.
Accordingly, a main object of the present invention is to provide an improved automatic self-cleaning print head that efficiently cleans the orifices and surrounding area of a print head.
More specifically, an object of the present invention is to provide an improved self-cleaning print head that cleans the front of the orifices regardless of the orientation of the print head.
Another object of the present invention is to provide an improved self-cleaning print head that effectively cleans out the inside of the orifices as well as their outer surfaces at the front face.
Yet another object of the present invention is to provide an improved self-cleaning print head that is easier to maintain due to elimination of manual work required to clean the print head.
Still another object of the present invention is to provide an improved self-cleaning print head that uses a relatively low amount of solvent for effective cleaning.
These and other objects of the present invention are discussed or will be apparent from the detailed description of the invention.
In keeping with one aspect of the present invention, a conduit supplies solvent to a front face of a drop generator near an orifice used for printing and then to a drain conduit. The drain conduit uses negative pressure to both maintain the solvent on the front face and to subsequently drain the solvent from the front face. This configuration creates a print head that can clean the front face of the drop generator regardless of the orientation of the print head, and without the aid of gravity.
More specifically, a print head for an ink jet printer that projects ink droplets to a substrate to be marked has a drop generator with a body that has a front face and at least one orifice extending through the front face. The orifice defines a nozzle for forming an ink filament and a stream of ink droplets. The print head also has a separate supply conduit for supplying solvent to the front face and a drain conduit for suctioning the solvent from the front face and into the drain conduit. Additionally, the supply conduit and the drain conduit have openings disposed relative to each other and the orifice so that the solvent released from the supply conduit moves along the front face, adjacent the orifice and into the drain conduit regardless of the spatial orientation of the print head.
In another aspect of the present invention, the print head has an extremely effective mechanism for cleaning the interior of the orifice on the front face of a drop generator as well as the main conduit that supplies the ink to the orifice for printing. This is accomplished by attaching a vacuum conduit to the main conduit just behind the orifice so that solvent located on the outside of the orifice on the front face of the drop generator is suctioned into the vacuum conduit through the orifice and the main conduit. This forces the solvent to flow completely through the orifice in the reverse direction of the ink flow through the orifice during printing.
In more detail, a print head for an ink jet printer that projects ink droplets to a substrate to be marked has a drop generator with a body that has a front face and at least one orifice extending through the front face. The orifice defines a nozzle for forming an ink filament and a stream of ink droplets. The print head also has a main conduit for supplying ink to the orifice and a supply conduit connected to a source of solvent for conveying the solvent through a supply opening and onto the front face. An orifice unclogging mechanism is also optionally supplied in the print head that forces the solvent disposed on the front face into the orifice so that the solvent flows through the orifice in the reverse direction. This structure effectively removes residue blocking an interior of the orifice with the solvent.
The present invention also includes a method of cleaning a print head for an ink jet printer. The process includes flowing solvent through a supply conduit to a front face of a body of the print head. The front face has a generally planar surface and at least one orifice extending through the front face. The orifice also defines a nozzle for forming an ink filament and a stream of ink droplets. The process further includes moving the ink along the front face adjacent the orifice, and suctioning the solvent from the front face into a drain conduit. The suctioning step removes solvent from the front face regardless of the orientation of the print head, with the solvent moving residue from the front face into the drain conduit.